A common difficulty encountered during the manufacturing of standard delivery systems is to provide encapsulation of the stored substance without voids or air bubbles. A standard process to avoid trapping air in a storage system or delivery system during assembly of the plunger of the system is to assemble the system under vacuum. However, a total absence of air cannot be achieved, so there will be a small amount of remaining air in the storage or delivery system. Furthermore, the use of a vacuum can also cause evaporation of the ingredients of the substance. The evaporation of ingredients may have a serious impact on the stored substance if the filling volume is very small, such as 1 ml or less, and if precise dosing is important, as with pharmaceutical products.
Another conventional process for filling a delivery system is to do so from the front end of the dispenser, which is the end through which the stored substance is dispensed. The plunger is thereby pushed backwards during filling. However, this process is limited to systems that allow filling from the front end.
U.S. Pat. No. 5,178,305 relates to a dispensing cartridge with a storage cylinder and a dispensing piston whose bottom surface facing the cartridge contents is progressively recessed towards an air evacuation bore. The evacuation bore is sealed by a closure.
WO 01/94028 relates to a ventilation device for a piston for a cartridge, comprising a first piston part which rests sealingly against the cartridge wall and a second piston part, which forms a valve together with the first piston part. Said valve opens when a pressure is exerted on the rear side of the piston so that the air that is trapped between the filling composition and the piston can escape. According to the invention, a filter section is provided in front of the valve, between the two piston parts, as seen from the flow path of the air through the valve. This filter section has at least one narrow channel which forms a penetration barrier for the filling mass and ensures that the valve remains dry and free of dirt.
Further reference is made to EP-A-0 344 491, EP-A-0 463 991, FR-A-2 626 248, EP-A-0 497 739, and U.S. Pat. No. 4,951,848.